This application claims the benefit of a Japanese Patent Application No.2001-040811 filed Feb. 16, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to signal reproducing methods and storage apparatuses, and more particularly to a signal reproducing method for improving a phase margin of a control system, and to a storage apparatus which employs such a signal reproducing method.
2. Description of the Related Art
In a storage apparatus employing a Redundant Array of Independent Disks (RAID) structure, a plurality of hard disk drives (HDDs) are provided. In such a storage apparatus, a situation frequently occurs where a write is carried out in an on-track state with respect to one HDD and a seek to a target cylinder is carried out with respect to another HDD, at the same timing. In this situation, vibrations of the HDD which is carrying out the seek may affect the HDD which is carrying out the write and cause an off-track state, to thereby deteriorate the performance of the storage apparatus.
Recently, the track per inch (TPI) has increased to increase the recording density of recording media in the storage apparatus. As a result, the off-track state is easily generated even by a small external disturbance. In addition, in order to realize a high-speed access by reducing the access time, a large current is applied in order to accelerate and decelerate a head, thereby increasing vibration applied to the head. Therefore, it is becoming essential to increase the operation band of the control system in order to suppress the external disturbances.
However, in a reproducing system of the storage apparatus, a computation process which generates a signal for controlling the head position inevitably includes a computation (or execution) delay. For this reason, a phase margin of the control system is used up by this computation delay, and there was a first problem in that it is impossible to simply increase the gain of the control system.
On the other hand, when the gain of the control system is simply increased, the phase margin is reduced, and there was a second problem in that a closed loop will oscillate.
In the prior art, there was also a third problem in that, as the velocity of the head increases, it becomes more difficult to quickly and accurately detect the head velocity.
Accordingly, it is a general object of the present invention to provide a novel and useful signal reproducing method and storage apparatus, in which the problems described above are eliminated.
Another and more specific object of the present invention is to provide a signal reproducing method and storage apparatus which can eliminate the first problem, the second problem and/or the third problem described above, by securing a phase margin of a control system.
Still another object of the present invention is to provide a signal reproducing method for reproducing servo information recorded on a recording medium by use of a head, comprising the steps of (a) carrying out a current calculation related to a current, and an observer calculation related to a position and a velocity of the head, based on reproduced servo information, and (b) calculating a current value for driving the head, based on a calculation result of the step (a), where the step (b) carries out only computations which require a demodulation result of a present sample during a first time after demodulation of the position of the head to a time when the current value is output, and carrying out computations which require a demodulation result of a past sample during a second time other than the first time. According to the signal reproducing method of the present invention, it is possible to eliminate the first problem described above.
A further object of the present invention is to provide a signal reproducing method for reproducing servo information recorded on a recording medium by use of a head, comprising the steps of (a) obtaining a prediction error by subtracting an estimated position of the head from an actual position of the head on the recording medium obtained from reproduced servo information, and (b) feeding back the prediction error to a control system which calculates a current value for driving the head. According to the signal reproducing method of the present invention, it is possible to eliminate the second problem described above.
Another object of the present invention is to provide a signal reproducing method for reproducing servo information recorded on a recording medium by use of a head, comprising the steps of (a) demodulating phase information which is included in the servo information for use in demodulating an actual position of the head on the recording medium, and (b) obtaining a velocity of the head based on a phase error of the phase information demodulated by the step (a). According to the signal reproducing method of the present invention, it is possible to eliminate the third problem described above.
Still another object of the present invention is to provide a signal reproducing method for reproducing servo information recorded on a recording medium by use of a head, comprising the steps of (a) demodulating phase information which is included in the servo information for use in demodulating an actual position of the head on the recording medium, (b) obtaining a velocity of the head based on a phase error of the phase information demodulated by the step (a), (c) obtaining the velocity of the head based on a present demodulated position and a previous demodulated position, and (d) employing the velocity obtained by the step (b) when the velocity of the head is greater than or equal to a predetermined value, and employing the velocity obtained by the step (c) when the velocity of the head is less than the predetermined value. According to the signal reproducing method of the present invention, it is possible to eliminate the third problem described above.
A further object of the present invention is to provide a storage apparatus comprising reproducing means for reproducing servo information recorded on a recording medium by use of a head, matrix calculation means for carrying out a current calculation related to a current, and an observer calculation related to a position and a velocity of the head, based on reproduced servo information, and filter calculation means for calculating a current value for driving the head, based on a calculation result of the matrix calculation means, where the filter calculating means carries out only computations which require a demodulation result of a present sample during a first time after demodulation of the position of the head to a time when the current value is output, and carrying out computations which require a demodulation result of a past sample during a second time other than the first time. According to the storage apparatus of the present invention, it is possible to eliminate the first problem described above.
Another object of the present invention is to provide a storage apparatus comprising reproducing means for reproducing servo information recorded on a recording medium by use of a head, means for obtaining a prediction error by subtracting an estimated position of the head from an actual position of the head on the recording medium obtained from reproduced servo information, and feedback means for feeding back the prediction error to a control system which calculates a current value for driving the head. According to the storage apparatus of the present invention, it is possible to eliminate the second problem described above.
Still another object of the present invention is to provide a storage apparatus comprising reproducing means for reproducing servo information recorded on a recording medium by use of a head, position demodulating means for demodulating phase information which is included in the servo information for use in demodulating an actual position of the head on the recording medium, and velocity obtaining means for obtaining a velocity of the head based on a phase error of the phase information demodulated by the position demodulating means. According to the storage apparatus of the present invention, it is possible to eliminate the third problem described above.
A further object of the present invention is to provide a storage apparatus comprising reproducing means for reproducing servo information recorded on a recording medium by use of a head, position demodulating means for demodulating phase information which is included in the servo information for use in demodulating an actual position of the head on the recording medium, first velocity obtaining means for obtaining a velocity of the head based on a phase error of the phase information demodulated by the position demodulating means, second velocity obtaining means for obtaining the velocity of the head based on a present demodulated position and a previous demodulated position, and means for employing the velocity obtained by the first velocity obtaining means when the velocity of the head is greater than or equal to a predetermined value, and employing the velocity obtained by the second velocity obtaining means when the velocity of the head is less than the predetermined value. According to the storage apparatus of the present invention, it is possible to eliminate the third problem described above.
Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.